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You searched for: creator:"D. W. Boukhvalov"
[texts]Enhancement of chemical activity in corrugated graphene - D. W. Boukhvalov
Simulation of chemical activity of corrugated graphene within density functional theory predicts an enhancement of its chemical activity if the ratio of height of the corrugation (ripple) to its radius is larger than 0.07. Further growth of the curvature of the ripples results in appearance of midgap states which leads to an additional strong increase of chemisororption energy. These results open a way for tunable functionalization of graphene, namely, depending of curvature of the ripples one c...
Downloads: 2
[texts]Tuning the gap in bilyaer graphene using chemical functionalization: DFT calculations - D. W. Boukhvalov
Opening, in a controllable way, the energy gap in the electronic spectrum of graphene is necessary for many potential applications, including an efficient carbon-based transistor. We have shown that this can be achieved by chemical functionalization of bilayer graphene. Using various dopants, such as H, F, Cl, Br, OH, CN, CCH, NH2, COOH, and CH3 one can vary the gap smoothly between 0.64 and 3 eV and the state with the energy gap is stable corresponding to the lowest-energy configurations...
Downloads: 2
[texts]Defect-induced ferromagnetism in fullerenes - D. W. Boukhvalov
Based on the ab initio electronic structure calculations the picture of ferromagnetism in polimerized C60 is proposed which seems to explain the whole set of controversial experimental data. We have demonstrated that, in contrast with cubic fullerene, in rhombohedral C60 the segregation of iron atoms is energetically unprofitable which is a strong argument in favor of intrinsic character of carbon ferromagnetism which can be caused by vacancies with unpaired magnetic electrons...
Downloads: 2
[texts]Chemical functionalization of graphene with defects - D. W. Boukhvalov
Defects change essentially not only electronic but also chemical properties of graphene being centers of its chemical activity. Their functionalization is a way to modify electronic and crystal structure of graphene which may be important for graphene-based nanoelectronics. Using hydrogen as an example, we have simulated a chemistry of imperfect graphene for a broad class of defects (Stone-Wales defects, bivacancy, nitrogen substitution impurity, and zigzag edges) by density functional calculati...
Downloads: 45
[texts]Chemical functionalization of graphene - D. W. Boukhvalov
Experimental and theoretical results on chemical functionalization of graphene are reviewed. Using hydrogenated graphene as a model system, general principles of the chemical functionalization are formulated and discussed. It is shown that, as a rule, 100% coverage of graphene by complex functional groups (in contrast with hydrogen and fluorine) is unreachable. A possible destruction of graphene nanoribbons by fluorine is considered...
Downloads: 2
[texts]Hydrogen on graphene: Electronic structure, total energy, structural distortions, and magnetism from first-principles calculations - D. W. Boukhvalov
Density functional calculations of electronic structure, total energy, structural distortions, and magnetism for hydrogenated single-layer, bilayer, and multi-layer graphene are performed. It is found that hydrogen-induced magnetism can survives only at very low concentrations of hydrogen (single-atom regime) whereas hydrogen pairs with optimized structure are usually nonmagnetic. Chemisorption energy as a function of hydrogen concentration is calculated, as well as energy barriers for hydrogen ...
Downloads: 2
[texts]Magnetism and local distortions near carbon impurity in $γ$-iron - D. W. Boukhvalov
Local perturbations of crystal and magnetic structure of $\gamma$-iron near carbon interstitial impurity is investigated by {\it ab initio} electronic structure calculations. It is shown that the carbon impurity creates locally a region of ferromagnetic ordering with substantial tetragonal distortions. Exchange integrals and solution enthalpy are calculated, the latter being in a very good agreement with experimental data...
Downloads: 2
[texts]Effect of local Coulomb interactions on the electronic structure and exchange interactions in Mn12 magnetic molecules - D. W. Boukhvalov
We have studied the effect of local Coulomb interactions on the electronic structure of the molecular magnet Mn12-acetate within the LDA+U approach. The account of the on-site repulsion results in a finite energy gap and an integer value of the molecule's magnetic moment, both quantities being in a good agreement with the experimental results. The resulting magnetic moments and charge states of non-equivalent manganese ions agree very well with experiments...
Downloads: 8
[texts]Correlation effects in the electronic structure of Mn$_4$ molecular magnet - D. W. Boukhvalov
We present joint theoretical-experimental study of the correlation effects in the electronic structure of (pyH)$_3$[Mn$_4$O$_3$Cl$_7$(OAc)$_3$]$\cdot$2MeCN molecular magnet (Mn$_4$). Describing the many-body effects by cluster dynamical mean-field theory, we find that Mn$_4$ is predominantly Hubbard insulator with strong electron correlations. The calculated electron gap (1.8 eV) agrees well with the results of optical conductivity measurements, while other methods, which neglect many-body effec...
Downloads: 3
[texts]Electronic structure of magnetic molecules V15: LDA+U calculations, X-ray emission and photoelectron spectra - D. W. Boukhvalov
Electronic structure of V$_{15}$ magnetic molecules (K$_6$ [V$_{15}$ As$_6$ O$_{42}$ (H$_2$O)] \cdot 8H$_2$O)$ has been studied using LSDA+U band structure calculations, and measurements of X-ray photoelectron (valence band, core levels) and X-ray fluorescence spectra (vanadium K$\beta_5$ and L$_{2,3}$, and oxygen K$\alpha$). Experiments confirm that vanadium ions are tetravalent in V$_{15}$, and their local atomic structure is close to that of CaV$_3$O$_7$...
Downloads: 1
[texts]Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-Ray Absorption, Emission, and Photoelectron Spectroscopies - V. R. Galakhov
Electronic structure of nickel nanoparticles encapsulated in carbon was characterized by photoelectron, X-ray absorption, and X-ray emission spectroscopies. Experimental spectra are compared with the density of states calculated in the frame of the density functional theory. The carbon shell of Ni nanoparticles has been found to be multilayer graphene with significant (about 6%) amount of Stone--Wales defects...
Downloads: 11
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